The present invention generally relates to a connection between an exhaust tubing and an exhaust port in the combustion engine casing and, more particularly, to a mounting of a tubular insert within the exhaust port to minimize or substantially eliminate a possible loss of heat of an exhaust gas flowing therethrough.
Specifically, the present invention pertains to an improvement in a combustion engine casing having at least one exhaust port in communication with combustion chamber within the engine casing, said exhaust port having a substantially tubular insert held in position within the exhaust port through a heat insulating member for minimizing or substantially eliminating any possible reduction in temperature of an exhaust gas to be exhausted through the exhaust manifold or tubing to the outside of the combustion chamber by way of said exhaust port.
In some of conventional combustion engines used, for example, in automotive vehicles, an exhaust gas purifying device, for example, a thermal reactor for reburning unburned components of the exhaust gas to substantially purify the latter, is installed in the exhaust system of the engine. Because of the nature and construction of the thermal reactor known to those skilled in the art, reduction of the temperature of the exhaust gas prior to said exhaust gas entering the thermal reactor does not ensure an efficient and effective re-combustion of the unburned exhaust gas components within the thermal reactor.
In order to avoid this, various methods have heretofore been employed and one of them is the use of a tubular insert installed within an exhaust passage leading from the combustion chamber to the exhaust port. The tubular insert extends from the plane of the exhaust port into the exhaust passage with its outer peripheral surface held in spaced relation to the surrounding wall, which has been left to define the exhaust passage, thereby minimizing or substantially eliminating any reduction of the temperature of the exhaust gas which may otherwise be effected by the influence of the temperature of the engine casing which is liquid-or air-cooled.
Structurally, the tubular insert heretofore used for the purpose described above has one end integrally formed with a radially outwardly extending annular flange through which said tubular insert is pressure-fitted into the exhaust port. This will now be described with particular reference to FIG. 1.
In FIG. 1, the engine casing is partially illustrated in section by 10. The combustion chamber 11 is in communication with the exhaust port, generally indicated by 12, through the exhaust passage 13 formed in the engine casing 10. As is well known to those skilled in the art, the combustion chamber 11 is selectively communicated and incommunicated with the exhaust passage 13 in a known manner by, for example, a poppet valve 14.
One of the opposed ends of the exhaust passage 13 which is remote from the combustion chamber 11 is radially outwardly enlarged in diameter to provide at least one support bore 13a into which the annular flange 15a of the tubular insert 15 is pressure-fitted with the body of said insert 15 extending into the exhaust passage 13 in spaced relation to the surrounding wall defining the exhaust passage 13.
In the conventional support structure for the tubular insert 15, the contact area between the engine casing 14 and the insert 15 is relatively so large that heat evolved in the tubular insert 15 in contact with the exhaust gas flowing therethrough tends to be transferred to the engine casing 10 through the flange 15a and then the support bore 13a. Consequently, a loss of heat occurs in the tubular insert 15 and the latter is somewhat cooled to a reduced temperature in substantial proportion to the amount of heat energies lost. As hereinbefore described, reduction in temperature of the tubular insert accompanies corresponding reduction in temperature of the exhaust gas flowing through the tubular insert 15. This is turn leads to reduction of the combustibility of the unburned components of the exhaust gas which are to be subsequently reburned in the thermal reactor.